Thanks Cameron. I’ll take a look.
During last night’s meeting a discussion on using Class C as an amplifier option was discussed.
There was additional discussion concerning BPSK and non-linear amplifiers.
After the meeting I reviewed BPSK. BPSK is a constant amplitude modulation and therefore can be amplified using non-linear amplification (Class C).
The difference in BPSK and FSK is the incorporation of phase shift keying between the two modulation frequencies rather than frequency shift keying as in FSK.
Actually it would be correct to refer to FSK as BFSK as both imply a shift between two frequencies.
I believe the confusion about BPSK is that it is often demodulated using SSB, more correctly slope detection as many demodulator systems to not support BPSK.
I’m not certain if there are Class C modules available and the availability of discrete RF transistors for 70cm and low power.
Jim McCullers
WA4CWI
Good evening,
I wanted to follow up on some of the PAs I've been looking at. They're ordered from most to least preferred. I'm not very experienced, so any advice will be well received!
* GRF5504 https://www.guerrilla-rf.com/products/DataSheet?sku=5504&file_name=GRF5504DS.pdf : P1dB of 34.3 dBm @ 460 MHz, so approximately the correct power levels. Very inexpensive and optimized for 70 cm applications (unlike many of the other options). The high gain (44 dB) may warrant less strain on the AX5043 PA and perhaps better performance out of the class E. Its main drawback is poor efficiency, which is expected to be around 50% @ 33dBm (see page 9). * MMG3006NT1 https://www.mouser.com/datasheet/2/302/MMG3006NT1-3138450.pdf : I'm a little skeptical of this device as all the measurements are taken at >900 MHz. We'd be using the device at its very lowest end of operation. At the measured frequency, performance is pretty good: P1dB = 33 dBm, 17.5 dB of gain, 2 dB higher NF than the former option. I'd want to test this device before implementing it on the board, as we'd be taking a risk using it at its lower end. * TQP7M9106 https://www.mouser.com/datasheet/2/412/QP7M9106-1500761.pdf : They really flaunt the high linearity and bandwidth of this amplifier, but it does have acceptable characteristics at the desired frequencies. Noise figure is around the same as the first option, and current consumption is between the other options.
I'm leaning towards the GRF5504 since it seems the most suited for the application, but maybe I'm wrong. There aren't a lot of good options in the 70 cm band. I can test it against a discrete amplifier on our PA test board.
I know we're sharing the antenna module with FOX+. Does anyone know how we're switching the resource to the antenna? Perhaps that's a question for the ICD manager. I wanted to suggest using MEMS switches since they're more reliable and take up less board space. We use them at work for our serializer channel switches. I'm not sure how they'll hold up at 2W, but they've proved better than relays in almost every sense. Here https://www.mdpi.com/1424-8220/24/10/3135 is a report on MEMS switches for antenna switching for space applications.
I also wanted to mention that I wrote a report https://docs.google.com/document/d/1N9ZAk-9m667yN1V_LVc1hHOa87ftJdjcrTFCgRIQQT0/edit?usp=drive_link on possible AX5043 replacements (not for an AMSAT group). I know it's not at the top of the list of things to do, but it might be a starting point for someone.
Thanks!
Cameron
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Cameron Castillo
KJ7ILB
P: (503) 752-8877
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